1. Field of the Invention
The present invention relates to an on-demand inkjet printing method and an on-demand inkjet printing device for printing characters and/or images for use in a printer, a plotter, a facsimile device, a copying machine or the like.
2. Description of the Prior Art
Printing devices such as printers are essential in the recent office automation environment, and even personal-use printing devices have been widely spreading. Among them, with respect to the printers, attention has been more paid to inkjet printers as compared with wire printers which perform printing by magnetically driving wires to press them onto a platen via an ink ribbon and a print medium such as a sheet of paper. As appreciated, as compared with the wire printer, the inkjet printer produces less noise and carries out high-speed printing with less printing cost per sheet.
In the inkjet printing, ink drops of different volumes or sizes are injected for forming dots of different sizes on a print medium so as to realize a halftone printing. In this case, the ink drops are jetted successively at constant periods (T[sec]).
Normally, the multi-pass printing is carried out wherein ink drops of the same size are successively jetted on one line, then ink drops of another same size are successively jetted on the same line, which are repeated to jet the ink drops of various sizes without changing the line.
In the foregoing halftone printing, however, there is a serious problem that a disorder of an output image is caused due to the fact that dots are not formed at predetermined positions on the print medium.
Although such a disorder of the output image is prevented in the multi-pass printing, there is a drawback that the printing speed is lowered.
The present inventors tried to seek the reason why the dots are not formed at the predetermined positions on the print medium, and found out that the ink drops hit upon the print medium at positions other than the predetermined positions due to differences in size of the ink drops. Specifically, when the ink drops of different sizes are injected, the flying speed increases as the volume or mass of the ink drop increases. As speed differences among the ink drops increase, the accuracy of the hit positions of the ink drops on the print medium is lowered to degrade the quality of the output image.
Therefore, it is an object of the present invention to provide an improved inkjet printing method that can eliminate one or more of the disadvantages inherent in the foregoing conventional techniques.
It is another object of the present invention to provide an improved inkjet printing device that can eliminate one or more of the disadvantages inherent in the foregoing conventional techniques.
According to a first aspect of the present invention, there is provided an inkjet printing method wherein ink drops injected from a nozzle one by one to be hit upon a print medium have at least two different sizes, the method comprising the step of changing an injection timing of the ink drop from the nozzle depending on the size of the ink drop to be injected.
It may be arranged that the ink drop having one of the at least two different sizes is set to be a reference ink drop for determining the injection timing and, when the ink drop to be injected is bigger than the reference ink drop, the injection timing thereof is delayed relative to a given drive period of the reference ink drop.
It may be arranged that the ink drop having one of the at least two different sizes is set to be a reference ink drop for determining the injection timing and, when the ink drop to be injected is smaller than the reference ink drop, the injection timing thereof is advanced relative to a given drive period of the reference ink drop.
As the size (volume) of the ink drop increases, the flying speed increases so that the ink drop reaches the print medium earlier. Therefore, if the injection timing is delayed correspondingly, the ink drop hits upon the print medium precisely at a target position. In contrast, as the size of the ink drop decreases, the flying speed decreases so that the ink drop reaches the print medium later. Therefore, if the injection timing is advanced correspondingly, the ink drop hits upon the print medium precisely at a target position. In this fashion, the accuracy of a hit position of the ink drop on the print medium can be enhanced to improve the quality of an output image.
According to a second aspect of the present invention, there is provided an inkjet printing method wherein at least two kinds of drive waveforms having different amplitudes are supplied depending on print data and an ink drop is injected from a nozzle by displacing a meniscus of ink in the nozzle according to each of the drive waveforms, the method comprising the step of changing an injection timing of the ink drop from the nozzle depending on the amplitude of the corresponding drive waveform.
In the foregoing first aspect of the present invention, the injection timing of the ink drop is determined depending on the size of the ink drop to be injected. Normally, the ink drop is injected by displacing the meniscus of ink in the nozzle so as to first retreat the meniscus from a tip of the nozzle and then suddenly force it forward. In this event, the size of the ink drop to be injected can be adjusted by changing the amplitude of the applied drive waveform to control the backward and forward displacement of the meniscus. Accordingly, the second aspect of the present invention defines the structure in terms of the displacement of the meniscus.
It may be arranged that the ink drop to be injected by the drive waveform having one of the different amplitudes is set to be a reference ink drop for determining the injection timing and, when the amplitude of the drive waveform for the ink drop to be injected is greater than the amplitude of the drive waveform for the reference ink drop, the injection timing thereof is delayed relative to a given drive period of the reference ink drop.
It may be arranged that the ink drop to be injected by the drive waveform having one of the different amplitudes is set to be a reference ink drop for determining the injection timing and, when the amplitude of the drive waveform for the ink drop to be injected is smaller than the amplitude of the drive waveform for the reference ink drop, the injection timing thereof is advanced relative to a given drive period of the reference ink drop.
As the amplitude of the applied drive waveform increases, the size of the ink drop increases so that the flying speed increases and thus the ink drop reaches the print medium earlier. Therefore, it is necessary to delay the injection timing correspondingly. In contrast, as the amplitude of the applied drive waveform decreases, the size of the ink drop decreases so that the flying speed decreases and thus the ink drop reaches the print medium later. Therefore, it is necessary to advance the injection timing correspondingly.
According to a third aspect of the present invention, there is provided an inkjet printing method wherein when ink drops are injected from a nozzle one by one, at least two kinds of pressure variations having different amplitudes are applied to ink in the nozzle, the method comprising the step of changing an injection timing of the ink drop from the nozzle depending on the amplitude of the pressure variation applied to the ink.
When injecting the ink drop by feeding the drive waveform to displace the meniscus of ink, the amplitude of the pressure variation applied to the ink upon injection differs depending on the amplitude of the drive waveform. Accordingly, the third aspect of the present invention defines the structure in terms of the pressure variation applied to the ink.
It may be arranged that the ink drop to be injected by the pressure variation having one of the different amplitudes is set to be a reference ink drop for determining the injection timing and, when the amplitude of the pressure variation for the ink drop to be injected is greater than the amplitude of the pressure variation for the reference ink drop, the injection timing thereof is delayed relative to a given drive period of the reference ink drop.
It may be arranged that the ink drop to be injected by the pressure variation having one of the different amplitudes is set to be a reference ink drop for determining the injection timing and, when the amplitude of the pressure variation for the ink drop to be injected is smaller than the amplitude of the pressure variation for the reference ink drop, the injection timing thereof is advanced relative to a given drive period of the reference ink drop.
As the amplitude of the pressure variation applied to the ink increases, the size of the ink drop increases so that the flying speed increases and thus the ink drop reaches the print medium earlier. Therefore, it is necessary to delay the injection timing correspondingly. In contrast, as the amplitude of the pressure variation applied to the ink decreases, the size of the ink drop decreases so that the flying speed decreases and thus the ink drop reaches the print medium later. Therefore, it is necessary to advance the injection timing correspondingly.
According to a fourth aspect of the present invention, there is provided an inkjet printing method wherein when ink drops are injected from a nozzle one by one, the ink drops have at least two different initial injection speeds, the method comprising the step of changing an injection timing of the ink drop from the nozzle depending on the initial injection speed of the ink drop to be injected.
Depending on the size of the ink drop to be injected, the initial injection speed of the ink drop also differs. Accordingly, the fourth aspect of the present invention defines the structure in terms of the initial injection speed of the ink drop.
It may be arranged that the ink drop to be injected at one of the two different initial injection speeds is set to be a reference ink drop for determining the injection timing and, when the initial injection speed of the ink drop to be injected is greater than the initial injection speed of the reference ink drop, the injection timing thereof is delayed relative to a given drive period of the reference ink drop.
For example, the injection timing is delayed by time_1 [sec] relative to the given drive period of the reference ink drop,
time_1=Lxc3x97|(1/v1)xe2x88x92(1/vxe2x80x94def)|
wherein L represents a distance [mm] from a tip of the nozzle to a print medium, v1 represents the initial injection speed [m/s] of the ink drop to be injected, and v_def represents the initial injection speed [m/s] of the reference ink drop.
It may be arranged that the ink drop to be injected at one of the two different initial injection speeds is set to be a reference ink drop for determining the injection timing and, when the initial injection speed of the ink drop to be injected is smaller than the initial injection speed of the reference ink drop, the injection timing thereof is advanced relative to a given drive period of the reference ink drop.
For example, the injection timing is advanced by time_3 [sec] relative to the given drive period of the reference ink drop,
time_3=Lxc3x97|(1/v3)xe2x88x92(1/vxe2x80x94def)|
wherein L represents a distance [mm] from a tip of the nozzle to a print medium, v3 represents the initial injection speed [m/s] of the ink drop to be injected, and v_def represents the initial injection speed [m/s] of the reference ink drop.
According to a fifth aspect of the present invention, there is provided an inkjet printing device comprising a drive waveform feed device for feeding at least two kinds of drive waveforms having different amplitudes depending on print data; a deform device which deforms according to the drive waveform fed from the drive waveform feed device; a pressure chamber which is supplied with ink and injects an ink drop via a nozzle by displacing a meniscus of the ink filled therein due to pressures applied to the ink and caused by deformation of the deform device; and a timing adjusting device which receives the amplitudes of the drive waveforms from the drive waveform feed device and adjusts a feed timing of the corresponding drive waveform to the deform device depending on the corresponding amplitude thereof, so that an injection timing of the ink drop via the nozzle is changed depending on the amplitude of the corresponding drive waveform.
The fifth aspect of the present invention deals with the device structure which can control an injection amount of the ink drop by controlling the amplitude of the drive waveform to control the meniscus displacement.
It may be arranged that the ink drop to be injected by the drive waveform having one of the different amplitudes is set to be a reference ink drop for determining the injection timing and, when the amplitude of the drive waveform for the ink drop to be injected is greater than the amplitude of the drive waveform for the reference ink drop, the timing adjusting device delays the feed timing of the drive waveform for the ink drop to be injected so that the injection timing thereof is delayed relative to a given drive period of the reference ink drop.
It may be arranged that the ink drop to be injected by the drive waveform having one of the different amplitudes is set to be a reference ink drop for determining the injection timing and, when the amplitude of the drive waveform for the ink drop to be injected is smaller than the amplitude of the drive waveform for the reference ink drop, the timing adjusting device advances the feed timing of the drive waveform for the ink drop to be injected so that the injection timing thereof is advanced relative to a given drive period of the reference ink drop.
The foregoing drive waveform feed device may be in the form of a specific circuit comprising digital-analog converters etc. or may be realized by a software control so as to feed the drive waveforms. Similarly, the foregoing timing adjusting device may be in the form of a specific circuit or may be realized by a software control. Further, the foregoing deform device may be in the form of a piezoelectric element, but is not limited thereto. Specifically, as long as it is subjected to deformation, such as expansion/contraction, shear deformation or bending deformation due to a bimorph effect, in response to applied voltage or the like, there is no particular limitation.
According to a sixth aspect of the present invention, there is provided an inkjet printing device comprising a drive waveform feed device for feeding drive waveforms; a deform device which deforms according to the drive waveform fed from the drive waveform feed device; and a pressure chamber which is supplied with ink and injects an ink drop via a nozzle due to pressure variation applied to the ink filled therein and caused by deformation of the deform device, the pressure variation having at least two kinds of amplitudes depending on the deformation of the deform device, wherein an injection timing of the ink drop via the nozzle is changed depending on the amplitude of the pressure variation applied to the ink.
The sixth aspect of the present invention deals with the device structure which can control an injection amount of the ink drop by controlling the amplitude of the pressure variation applied to the ink.
It may be arranged that the ink drop to be injected by the pressure variation having one of the amplitudes is set to be a reference ink drop for determining the injection timing and, when the amplitude of the pressure variation for the ink drop to be injected is greater than the amplitude of the pressure variation for the reference ink drop, the injection timing thereof is delayed relative to a given drive period of the reference ink drop.
It may be arranged that the ink drop to be injected by the pressure variation having one of the amplitudes is set to be a reference ink drop for determining the injection timing and, when the amplitude of the pressure variation for the ink drop to be injected is smaller than the amplitude of the pressure variation for the reference ink drop, the injection timing thereof is advanced relative to a given drive period of the reference ink drop.
According to a seventh aspect of the present invention, there is provided an inkjet printing device comprising a drive waveform feed device for feeding drive waveforms; a deform device which deforms according to the drive waveform fed from the drive waveform feed device; and a pressure chamber which is supplied with ink and injects an ink drop via a nozzle due to change in internal volume of the pressure chamber caused by deformation of the deform device, the volume change having at least two kinds of amplitudes depending on the deformation of the deform device, wherein an injection timing of the ink drop via the nozzle is changed depending on the amplitude of the volume change.
The seventh aspect of the present invention deals with the device structure which can control an injection amount of the ink drop by changing the volume of the pressure chamber filled with the ink to control the amplitude of the pressure variation applied to the ink.
It may be arranged that the ink drop to be injected by the volume change having one of the amplitudes is set to be a reference ink drop for determining the injection timing and, when the amplitude of the volume change for the ink drop to be injected is greater than the amplitude of the volume change for the reference ink drop, the injection timing thereof is delayed relative to a given drive period of the reference ink drop.
It may be arranged that the ink drop to be injected by the volume change having one of the amplitudes is set to be a reference ink drop for determining the injection timing and, when the amplitude of the volume change for the ink drop to be injected is smaller than the amplitude of the volume change for the reference ink drop, the injection timing thereof is advanced relative to a given drive period of the reference ink drop.